Why was I charged for more than the price shown by iTunes App Store?

Depending on where you live, the applicable sales tax may be added to the charge.

iTunes App Store bundles purchases from multiple days into one payment, so it could be that you've made other purchases in the game, or in other apps, via App Store around the same time and have been charged for all of them together. Please check your purchase history in iTunes to see if this explains the issue and see this Apple Support page for further information: https://support.apple.com/en-us/HT201382